Ferric Chloride or Muriatic Acid + Hydrogen Peroxide for etching?

I've switched from FeCl to acid/hydrogen peroxide exclusively, in my experience it has an extremely short shelf life but considering how cheap it is that hardly matters, the main benefits are etching speed and results, FeCl takes 3 to 4 times longer than a new batch of acid/hydrogen peroxide and with the latter I've done tracks down to 0.2mm with no problems.

I've used the muriatic acid/hydrogen peroxide solution. It works great when it's fresh, but it does NOT keep for me. If I go back and use it a couple of weeks later, it just doesn't work. I haven't pursued proper disposal, yet, so I've accrued a bit of the stuff in mason jars (whose lids are rusting from the acid, by the way). Once I figure out how to get rid of the acid/peroxide mixture, I think I'm going to try FeCl.

Can't comment on that specific combo but I know that some alternatives have poor shelf life of made-up solution. FeCl solution lasts indefinitely. The biggest downside of FeCl is that it stains.